Power viscous material dispensers such as caulking guns that are driven by various power sources such as compressed air or electric motors are well known in the art. One commercially successful power caulking gun is disclosed in U.S. Pat. No. 5,775,539 to Bates et al., which is incorporated herein by reference in its entirety. The caulking gun described in the '539 patent includes an electric motor that drives a piston carrying rack through a combination of planetary, bevel, and pinion gears. The electric motor is retained in a housing that protrudes from the rear of the gun and the motor shaft rotates about an axis that is parallel to the length of the piston carrying rack.
Many adhesive materials are sold as two constituent materials, or parts, that are mixed together upon application to form a single adhesive material. Electric dispensing guns have been developed to dispense two part adhesives. For example, U.S. Pat. No. 6,089,407 to Gardos describes a fluid material dispensing gun for dispensing two part materials for dental use that has in-line longitudinal racks for driving a piston into each of the constituent fluids, which are then concurrently dispensed through a single orifice. This dispensing gun has racks that are driven by an electric motor through a series of bevel gears and a pinion gear that rotates about an axis perpendicular to the axis of rotation of the motor.